Which bodies are you using for thin sweeping? Have you tried checking the aspect ratio for these bodies?
you may need to reduce the surface mesh size, if it is too much for mesh to be successful. https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v231/en/wb_msh/msh_specialized_thin_model_sweep.html
-Aniket
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